The present invention relates to evaporating or condensing on surfaces and in particular to an application of evaporating and condensing to surfaces in heat pumps.
A liquid layer, as it, for example, occurs in an evaporator of a heat pump, executes, due to the typical layering which may be observed with liquids and in particular with water as an operating liquid, a heat distribution which means that in the evaporator the top portion is cooled while the bottom portion of the layer virtually has the same temperature as the operating liquid as it is supplied from a heat source.
With condensers for heat pumps the situation is similar. Here, the compressed and thus heated-up vapor of operating liquid, like, for example, water vapor, when water is used as the operating liquid, meets a “cold” liquid layer. This leads to only the surface of the liquid layer being heated up in the condenser while the bottom portion of the liquid layer in the condenser which is not directly in contact with the vapor is not heated up.
Apart from that, with the evaporator of a heat pump there is still the problem that the compressed and heated-up vapor may be overheated, which means that in spite of the fact that the vapor meets the liquid to be heated up the heat transmission from vapor into liquid is limited.
All of these problems lead to the fact that the efficiency when evaporating or condensing is reduced. In order to still generate a heat pump, for example with sufficient power, thus the cross-sectional area of the evaporator or the cross-sectional area of the condenser has to be very large.